In precast or poured-in-place voided concrete shapes, disposable internal void forms are used, which are either rectangular or circular in cross section and are made out of corrugated paper, wound solid fiber, wood or expanded polystyrene. These void forms remain in the shape after it is cast. In order to vent accumulated moisture and methane gas which is sometimes generated in the void, it is necessary to provide void drains.
A void drain of the prior art is shown in U.S. Pat. No. 3,344,567. This is placed on the upper portion of the base form and is held in place by longitudinally extending steel strands adjacent the bottom of the shape which provide the necessary reinforcing in the shape. The strand itself, resting on shoulders of the void drain, can hold the void drain in place or a wire can be used to hold down the void drain between two strands. The void form rests on top of a plurality of the void drains prior to pouring the concrete. Since the top of the void drain tube is merely in contact with the undersurface of the void form, it is necessary to have the top of the void drain tube closed to prevent concrete from entering the void drain tube between any space that might exist between the top of the void drain tube and the bottom of the void form. Thus, the upper end of the tubular drain portion of the void drain is an integral cover and after the completion of the manufacture of the beam, the cover is opened by punching a hole through the frangible knock-out cover of the void drain and then through the void form thus permitting draining of water and any gas that accumulates therein. Such a void drain of the prior art may be used with void forms that are both rectangular and circular in cross section. However, in order properly to position them, the circular cross-sectional forms must be otherwise supported with wires, etc., since prestressing strands do not normally occur directly under the circular void forms and are not present at all in poured-in-place voided concrete shapes. Therefore the void drains represented by U.S. Pat. No. 3,344,567 are not particularly well suited for use with round void forms for poured-in-place voided concrete shapes.